In integrated circuit fabrication, metal lines (such as copper lines) are typically embedded in ILD layers, where the ILD is often a porous silicon oxide based dielectric material or an organic polymeric dielectric material having a low dielectric constant, such as an ultra-low-k (ULK) dielectric with a dielectric constant of 2.2 or less. Formation of such embedded metal lines via a Damascene process requires patterning and etching of the ILD to form vias and trenches, followed by filling of these vias and trenches with a metal (e.g., copper), for example, using electroplating. After the vias and trenches are filled with a metal, a second layer of ILD is deposited and is again patterned to form vias and trenches. These recessed features are again filled with a metal, such that a stack of ILD layers having embedded metal lines is formed, where the metal lines form the conductive paths of an integrated circuit. Etch stop layers are often deposited over individual ILD layers and metal lines, and are used in patterning operations of the IC fabrication process to protect the material residing underneath these layers from being etched during patterning. For example, the semiconductor substrate may include an etch stop layer residing between two ILD layers. When the top ILD layer is patterned and etched (e.g., with a fluoride-based chemistry) to define vias and trenches, the etch stop layer protects the bottom ILD layer underneath the etch stop from being etched.
The material of the etch stop layer should exhibit good etch selectivity versus the material that is being etched. In other words, the etch stop layer material should be etched at a significantly lower rate than the exposed ILD material (or other material that is being patterned).
Etch stop layers typically are not completely removed during the integrated circuit fabrication, and remain in the final manufactured semiconductor device as thin films between thicker ILD layers. Examples of conventionally used etch stop layer materials include silicon carbide and silicon nitride.